1. Field of the Invention
The present invention relates to a vane-type valve timing control apparatus and control method for an internal combustion engine. More specifically, the invention relates to a vane-type valve timing control apparatus having a resilient member for urging the vanes secured to the cam shaft toward the advance angle side or the delay angle side, and control method.
2. Related Art of the Invention
As a vane type variable valve timing control apparatus, there is one heretofore disclosed in Japanese Unexamined Patent Publication Nos. 10-141022 and 10-068306.
With this apparatus, recess portions are formed on an inner peripheral face of a cylindrical housing secured to a cam sprocket, while vanes secured to a cam shaft are accommodated in the recess portions, the construction being such that the cam shaft can rotate relatively with respect to the cam sprocket, within a range in which the vanes can move inside the recess portions.
Furthermore, the construction is such that by supplying and discharging oil by means of a spool valve, relatively with respect to a pair of hydraulic chambers (advance angle side hydraulic chamber and delay angle side hydraulic chamber) formed by the vanes partitioning the recess portions into front and rear in the rotation direction, the position of the vanes in the recess portions is changed, thereby enabling a rotation phase of the cam shaft relative to a crank shaft to be continuously changed.
A control value of the spool valve is determined by adding a feedback correction value set depending on a deviation of an actual rotation phase from a target value, to a constant neutral control value (basic control value) for retaining a rotation phase. A dither signal is then superimposed on the determined control value which is then output to an actuator of the spool valve.
However, as disclosed in Japanese Unexamined Patent Publication No. 10-068306, in the case where a resilient body such as a spiral spring for urging the vane to the advance angle side or to the delay angle side is provided, the urging force of the resilient body varies due to the rotation phase. Therefore, the response characteristic in the feedback correction of the rotation phase varies depending on the rotation phase and the direction of change thereof, causing a delay in the response to a particular change in the rotation phase.